This disclosure relates to an ambient pressure turbine for production of efficient power from water flow heads of relatively small size. It accommodates substantial water flow and low available heads.
Turbines conventionally are classified in two primary groups, reaction turbines and impulse turbines.
The reaction turbines include the Kaplan type or propeller turbine, which is similar to the propeller of a ship operating in reverse. Water flows through the turbine and causes the propeller to rotate. The water rotates axially through the propeller and such turbines are typically referred to as axial-flow turbines. Francis or radial-flow turbines are a pressure differential turbine and divert water at right angles to the direction of entry, causing the turbine rotor to revolve. Water fills an entrance volute which surrounds the runner and then flows between fixed guide vanes to enter the runner and flow toward its center. The guide vanes largely convert the water energy into rotary motion. The vanes and runners are typically filled with flowing water and a relatively high head is required for efficient operation.
Impulse type turbines are velocity differential turbines and are represented by the Pelton wheel, which utilizes jets of water directed at cups or buckets on the periphery of a water wheel.
The present improvement uses principles involved in both reaction and impulse type turbines. In common with reaction type turbines, the water flow changes radius and direction, resulting in centrifugal forces. In common with the impulse type turbine, one of the determinants of the amount of elevation of the water on the vanes is the difference between the forward speed of the rotating vane and the velocity (under ambient pressure) of the flow entering the runner. These reaction and relative velocity characteristics are closely interrelated in the operation of the present turbine. However, by utilizing supercritical flow conditions at the vane, efficient power transfer from a volute to a runner vane is accomplished under head requirements not practically suitable for existing turbine designs.